There are number for things to keep in mind when moving cars between the two countries, for the purpose of buying or selling. Rgardless of "Free Trade" the automotive industry is highly regulated, not just to protect jobs, but consumers and the environment.

Sometimes the cars are different in each country: For example, California requires special anti-pollution systems to be in place, and Canada (by virtue of our cold winters) requires block heaters.

Here is some information for importing vehicles into Canada or taking a Canadian vehicle into the US: